Reflex depressed collector

ABSTRACT

A reflex depressed collector is disclosed which facilitates electron collection on plural electron collecting surfaces in row form without adverse effects of electron reflection or back streaming. An electron beam passes by the collectors and then is radially dispersed by an electrostatic field so that electrons are given curving trajectories wherein they are first slowed to an essentially zero forward velocity and then slightly reaccelerated in a different direction before being collected on surfaces of the electrodes exposed to the beam after the beam passes thereby. The electrodes operate at a voltage lower than that which originally accelerated the stream, therefore the waste heat delivered to the collector is reduced and the power conversion efficiency of the device to which the collector is attached is increased.

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[54} REFLEX DEPRESSED CULLECTU [72] Inventors: Thore G. Milhran, Schenectady; Wendell Neugebauer, Ballston Spa, both of NY.

[73] Assignee: General Electric Company [22} Filed: Oct. 23, 1969 [21] Appl.N0.: 860,724

[52] U.S.Cl... ..315/5.38,315/3.5 [51] lnt.CI ..ll-l0lj 23/02 [58] lfieldofSearch ..3l5/5.38, 3.5

[56] References Cited UNITED STATES PATENTS 3,453,482 7/1969 Preist ..315/5.38 X 2,610,306 9/1952 Touraton et a1. ...315/5.38 X 2,325,865 8/1943 Litton ..315/5.38 3,153,743 10/1964 Meyerer ..315/5.38 3,172,004 3/1965 Gutfeld et a1. ...315/5.38 X 3,368,104 2/1968 McCullough ..315/5.38

[ 1 Feb.22,1972

3,271,618 9/1966 Kooyers ..315/5.38 X

Primary ExaminerHerman Karl Saalbach Assistant ExaminerSaxfield Chatmon, Jr.

Att0meyNathan J. Comfeld, Frank L. Neuhauser, Oscar B. Waddell, Joseph B. Forman and John P. Taylor [5 7] ABSTRACT A reflex depressed collector is disclosed which facilitates electron collection on plural electron collecting surfaces in row form without adverse effects of electron reflection or back streaming. An electron beam passes by the collectors and then is radially dispersed by an electrostatic field so that electrons are given curving trajectories wherein they are first slowed to an essentially zero forward velocity and then slightly reaccelerated in a different direction before being collected on surfaces of the electrodes exposed to the beam after the beam passes thereby. The electrodes operate at a voltage lower than that which originally accelerated the stream, therefore the waste heat delivered to the collector is reduced and the power conversion efficiency of the device to which the collector is attached is increased.

14 Claims, 4 Drawing Figures 0-7 xv SUPPLY 20 TKV r ZAMP F SUPPLY BIAS SUPPLY 28 PATENTEDFEBZZIQYE 3.644.778

SHEET 1 or 2 -26 [7M SUPPLY r 2 AMP J,

; SUPPLY BIAS SUPPLY INVENTORS rHEODORE G. MIHRAM WENDELL NEUGEBAUER THEIR ATTORNEY.

PATENTEDFEB22 m2 3. 644,778

SHEET 2 OF 2 INVENTORS: THEODORE e. MIHRAN WENDELL NEUGEBAUER HEIR ATTORNEY.

REFLEX DEPRESSEI) COLLECTOR The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of I958, Public law 85-568 (72 Stat. 435; U.S.C. 2457). Rights to practice the invention for any use primarily related to aeronautical and space applications are available through the National Aeronautics and Space Administration.

1. Field of the Invention This invention relates to reflex depressed collectors and more particularly to electron collectors which reflect electrons from a given electron beam and collect these electrons, on electron trajectory oriented electrodes, after they have reached the lower velocity apex of their trajectories, and with a slight acceleration effect.

2. Description of the Prior Art Electron beam devices, such as for example klystron amplifiers, traveling wave tubes, and grid controlled tubes generally, employ some means of collecting an electron beam therein, These electron collectors are usually in the form of metallic surfaces of revolution, for example, cup shaped, conical, cylindrical, etc., and are operative at a positive potential with respect to the potential of the cathode which provides the electron beam. Accordingly, electrons from the electron beam after passing through the particular beam device are then collected on the surface of the collector.

These collectors are particularly characterized in that they collect electrons by generally forward impact of the electron on the collector, usually with the collector interjected into or otherwise being in opposition to the generally forward trajectory of the electrons from the beam source through the device and into the collector. Because the collector is usually operated at a ground or positive potential, the electrons from the electron beam strike the collector with considerable energy so that collector temperature is increased and deleterious secondary emission of electrons from the collector takes place.

It is known in the prior art that a collector need not necessarily be operated at ground potential or zero volts with respect to the cathode, but may be operated at a half voltage with respect to the cathode, for example at a less negative potential with respect to the cathode; i.e., it is positive with respect to the cathode. Therefore, both the cathode and the collector are operating at different negative potentials, and it has been found that far less power is utilized in providing the electron beam of the required velocity. Such collectors are known as depressed collectors.

A depressed collector still has the disadvantage that electrons continue to strike the collector with sufficient force to cause secondary emission of electrons from the collector surfaces. These secondary electrons find their way back into the electron beam to cause serious oscillations together with incipient instability due to electrons traveling backwards through the device. Secondary or returned electrons also cause heating of fragile high frequency parts of the structure.

Accordingly, it is an object of this invention to provide an electron collector having reduced secondary electron characteristics,

It is a further object of this invention to provide an electron collector device having inherent secondary electron collection characteristics therein.

It is yet another object of this invention to provide an electron beam collector to collect electrons from an electron beam without substantial interception of the forward trajectory of the beam.

It is another object of this invention to provide means to alter the direction of electrons moving in a beam so that collection of these electrons may take place after the trajectory apex of the beam has been reached.

It is a further object of this invention to provide a reflex depressed collector having an axially spaced array of collector electrodes in combination with a central reflector so that electrons from electron beam pass by the electrodes, are reflected by the reflector, and collected on the back surfaces of the electrodes, after the apex or direction reversal by means of the reflector takes place.

SUMMARY OF THE INVENTION This invention in one ofits preferred forms includes an electron beam device having a collector housing structure at one end. The housing includes a spike or body member projecting coaxially in a direction in opposition to the electron beam direction to reflect electrons of the beam in a generally reverse direction radially away from the body member. Coaxially surrounding the projecting body and the beam path in the housing are a plurality of axially spaced transverse or radially inwardly projecting surfaces and arranged to collect the reflected electrons after their apex has been reached.

BRIEF DESCRIPTION OF THE DRAWING This invention will be better understood when taken in connection with the following description and the drawings in which:

FIG. 1 is an illustration of one preferred embodiment of this invention as part of a klystron-type amplifier.

FIG. 2 is an illustration of a further preferred collector as-' sembly.

FIG. 3 is an illustration of a modified collector assembly. FIG. 4 is an illustration of a further modified collector assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention may be best described with reference to an exemplary device such as the klystron device of FIG. 1. Referring now to FIG. 1, there is shown in schematic form a klystron device 10 including a cathode 11 which supplies an electron beam 12 passing through a series of cavity resonators l3, l4 and 15, to be collected by a collector l6. Klystron 10 may also be various other electron beam devices including, for example, traveling wave tubes, crossfield tubes, amplifiers, oscillators, and other beam-type electron devices. In FIG. 1, the beam represented at 12 is exemplary in that a beam passing through a beam device as noted above begins to flare circumferentially outwardly after passing through the device and moving into the collector such as collector 16. This outward flaring has three causes the electrons repel each other due to their own space charge; there is a radial component of the electrostatic fields caused by potentials on the collector electrodes; and the beam device is usually surrounded by a collimating or focusing magnet whose lines of force also flare outwardly at about the collector location.

In FIG. 1, housing 17 of collector 16 is insulated from tube body 18 at 19 so that the electrical potential applied thereto may be different from electrical potential applied to the tube body. As shown in FIG. 1 for example, the tube body is at ground potential at ground 20 while the collector 16 is at a negative potential with respect to tube body 18, and is in fact at or near the same negative potential as the cathode 11. The difference in potential of the cathode l1 and the tube body 18 provides the driving force and velocity of the electron beam through the klystron 10.

Collector assembly 16 which usually surrounds and defines a part of the beam path, utilizes a central-projecting member 21 which faces into the path of the electron beam 12 and is tapered in a spike like or needle shape in combination with a series of coaxial apertured collector electrodes 22 to provide proper reflection and collection characteristics.

Central-projecting member 21 is an elongated spike like or needle-shaped reflector electrode which projects significantly into the beam path from housing 17. The extent of penetration and the particular taper may best be chosen with respect to the beam density and velocity of a given tube type, as well as the complementary configuration of the collector electrodes 22. Spike member 21 is electrically insulated from the collector housing 17 by an insulator seal 24 and may therefore have different potentials applied thereto. In one practice of this in vention and potential of spike member 21 has been varied from the same potential as the collector 16 to a more negative potential by means ofa separate power supply 26. In coaxial relationship with spike member 21, there is provided a spaced axial series ofdishlike or plate collector electrode members 22 having a central aperture 23 therethrough defining a path for the electron beam 12. Each of the collector electrodes are electrically insulated from each other and from the collector housing 17 and are connected through appropriate resistance 25 to a power supply 27 so that different potentials may be applied thereto. The circuit would preferably include separate power supplies to the different electrodes. In one preferred embodiment of this invention, each of the collector electrodes 22 is provided with a negative potential with each succeeding electrode 22, in a direction away from cathode 11, being at a potential more negative than the preceding electrode, or in other words each succeeding electrode is at a less positive potential with respect to the preceding electrode.

Ordinarily, housing 17 would be connected in the required circuit so that a negative potential could be applied thereto which is more negative with respect to the collector electrodes. In this instance, as a practical matter housing 17 would be enclosed in a further housing which would be operative at ground potential. Housing 17 would then serve as a shield member.

In operation of the FIG. 1 device with power supplies 26, 27 and 28 in operation, the electron beam 12 passes through the klystron device on its way to collector 16. Appropriate voltages are set for this operation in the usual manner for klystron operation and with the various potentials as described. As the beam approaches spike member 21 which is at a more negative potential with respect to the collector electrodes 22, electrons begin to be deflected radially to have an outward flare as previously described. The combination of electron momentum and electron deflection, and the presence of collector electrodes at less negative potential than the spike member 21 causes these electrons to follow a backwardly curving trajectory, such as illustrated in FIG. 1. These trajectories include an almost complete reversal of electron direction in many instances, and in most instances a defined apex which represents a significant reduction in forward electron velocity. The principle of reflex collection requires that the electrons from the beam not be collected until after their point of deepest penetration into the collector assembly, which would be the apex oftheir trajectories.

Collection of electrons takes place in a very different manner as compared to forward intercept-type collectors. The reflected electrons are caused to have radial trajectories which curve to provide some reversal of the original forward direction. Consequently, these electrons impinge on the back or rear surface 29 of electrodes 22 as differentiated from the front or beam facing surfaces 30. As can be seen in FIG. 1, the front surfaces 30 are those surfaces first approached by the electron beam in passing through or by the collector electrodes. The back or rear surfaces 29 are exposed to the electron beam after the beam has passed through or by the collector electrodes. Impingement of electrons on the rear surfaces takes place shortly after the trajectory apex is reached which is the point oflowest forward velocity ofthe electron. An electron in the beam is reflected radially and rearwardly so that it approaches the rear collector surfaces on a collision course but with much reduced velocity. Secondary electron emission from the rear side of the electrodes is suppressed because of low impingement velocity and particularly because a secondary electron in that area sees mostly an adjacent electrode of more negative potential from which it is reflected to its original electrode. Some electrons are caused to strike and be collected by the front surfaces of the collector electrodes but their number is not a significant part of the electron beam. These electrons merely go to the next more positive electrode and are not returned down the main body of the tube. Computer studies show that most of the electrons, at least about 90 percent, are collected on the back surfaces 29 of electrodes 22. Proper voltage distribution and spike 21 penetration minimizes forward intercept collection.

Not all electron trajectory apexes appear in the same axial position since all electrons emerging from an electron beam device such as a klystron do not have the same velocity. Accordingly, a number of collector electrodes are employed in axial spaced relationship along the beam path to maximize electron collection for different trajectories. These electrodes 22 are preferably of a flared, frustoconical, or otherwise concave configuration and are generally positioned in a concave manner with respect to the beam source. The collector surfaces of electrodes 22 need not be smooth but may be suitably roughened or of various cross-sectional configurations such as curved, corrugated, waffled, and apertured as for example, a single or plural mesh construction. Electrodes 22 may have different size central apertures 23 therethrough which define an outwardly tapering path to follow the general outwardly flaring surface of the beam 12. This beam flare and the cor responding different opening sizes may define an involute curve path for the beam.

The collector electrodes 22 are so arranged and constructed that not only do their central apertures 23 define successively the flare of the beam 12, but also they are positioned and spaced, in general, along the beam path in the collector to accommodate regions of varying reflected electron densities. The actual spacing between collector electrodes 22 as well as the number of electrodes to be employed is a design criteria appropriate to tube requirements; i.e., size of beam, beam density, beam velocity, and efficiency. The spacing between electrodes may vary, if necessary, to provide maximum collection where return beam density is the greatest. Empirically, good results are attainable with electrode axial spacing from about 0.25 to 0.50 inch for an L-band, 3 kilowatt tube. Different spacing may be employed in traveling wave tubes than in klystron tubes.

It is preferable to have the collector electrodes 22 extend at an angle to the beam direction as illustrated in FIG. 1, an angle between about 0 to 60 being preferable, measured from a line perpendicular to the beam path, the beam path subtending the angle in the direction of the beam. The radial dimension of these electrodes 22 is also dependent on beam density and size as well as the degree of electron reflection dispersal required.

Various air or fluid cooling means may be applied to the collector assembly 16 generally, or to specific parts such as the collector electrodes 22 or spike member 21. Cooling means are desirable for the spike member 21 since it is likely to be subjected to some direct electron bombardment. In one practice ofthis invention, spike member 21 is a hollow conical member having an inwardly projecting tube 31 through which a suitable coolant flows to contact the interior spike member 21.

Trajectories of both primary and secondary electrons were plotted from computer results. A resistor network with current injection sources to simulate space charge was used to solve Poisson's equation in the collector. Electron trajectories in the resulting field were computed automatically by a general purpose precision analog computer connected to the network. Computer results indicate that there is a focusing action ofthe collector on the electrons which enter the collector with varying velocities as well as directions. This focusing action is noted after the electrons have been reflected, i.e., after their apexes have been reached. Accordingly, the size, shape, number, and spacing of collectors may be determined for different tube types or different beam characteristics, or for predetermined classes of tubes or beam types. This precision kind of determination provides incremental advantages. Substantial advantages are attained by ordinary empirical relationships.

A number of embodiments of the depressed reflex collector of this invention may be utilized to good advantage for a number of different beam-type devices. Such devices may include noncoaxial relationships where, for example, the beam passes by a vane like array or row of collector electrodes and the beam is reflected so that reflex collection occurs. In this instance, the reflection may only be in one direction or over 180 rather than 360 as described in FIG. 1. A particular operative embodiment for klystron tubes is illustrated in FIG. 2. Referring now to FIG. 2, there is shown a depressed collector assembly 32 as adaptable to klystron application. Collector 32 includes a housing means 33 which, for the purposes of clarity, is illustrated as joined to the terminal drift tube part 34 of klystron. Housing 32 is joined to tube part 34 through the medium of a well-known ceramic to metal insulating and lead through seal 35. Housing 32 is therefore electrically insulated from tube part 34 and may be operative at ground potential. Housing 33 includes therewithin a shield member 36 which is similar to housing 17 of FIG. 1. Shield 36 is cup shaped and supported from housing 33 in electrical insulating relationship by supporting means 37 passing through seals 38. Accordingly, shield 36 may be operated at negative potential while housing 33 is at ground potential.

Projecting through housing 33 andshield 36 in axially opposed relationship to the beam and beam path is a spike member 39. Spike member 39 is also positioned in cover 33 by means of a lead through seal 40 which is similar to lead through seals and 38. Spike member 39 includes a projecting body portion 41 having a very high-temperature resistant end tip 42. A suitable metal for end tip 41 is molybdenum or tungsten, although under proper conditions, other refractory metal and combinations thereofmay be gainfully employed.

It is usually desirable to provide cooling for the spike member 39 since end tip 41 particularly and body portion are subjected to some electron as well as positive ion bombardment. Accordingly, a suitable coolant such as water may ,be circulated into the interior of spike member 39 through coolant tube means 43.

A series of collector electrodes 44 through 47 are sealed to a wall portion 48 of housing 33. Wall portion 48 includes a series of ceramic to metal seal members 49 supporting the collector electrodes in insulating relationship with respect to housing 33. Therefore, the described arrangement provides a series of collector electrodes which are electrically insulated from each other as well as from housing 33.

In a preferred embodiment of this invention, the illustrated collector electrodes 44 through 47 define in cross section a petal opening like arrangement where the nearest electrode 44 includes a surface near perpendicular to the beam path 12, and the furthest electrode 47 includes a major surface at about 40-60 to the axis of beam path 12. The distance between individual collector electrodes may vary from one electrode to an adjacent electrode along their edges which define the beam path 12. As illustrated in FIG. 2, the distance between electrodes 44 and measured at the beam path edge is different from the distance between electrodes 45 and 46 also measured at their beam path defining edges. The distance between electrodes 46 and 47 is significantly larger. Various combinations of varying distances may be employed within the scope of this invention. More particularly, the electrodes are spaced in correlation with electron trajectories and densities to take maximum advantage of collection efficiency.

The edges of the electrodes which define the beam path may best define a path which at least tapers outwardly to conform generally with the naturally curving or flaring of the beam. Such a curve may range from a straight line taper to parabolic or involute curves. In this manner, the electrodes are utilized to their best electron receiving efficiency.

The spike member 39 extends into the beam path defined by the electrodes 44-47 to a point about midway therein. The spike body is utilized in cooperative relationship with the electrodes to define a proper beam path and flaring characteristics, and to provide increased electron collecting efficiency. Accordingly, the taper of spike member 39 may closely follow the taper of the beam path 12 defined by the electrodes 44-47, However, the shape or taper of spike member 39 is of lesser significance than the shape or taper of the electrodes utilized to define the beam path.

It is an important feature of this invention that with the proper potential applied to the spike member 39, the shield 36 and to the individual collector electrodes 44-47, the flaring trajectory of beam 12 is controlled so that a significant number of electrons, usually in excess of to percent of the available electrons in the beam are caused to follow trajectories similar to those indicated by dash lines in FIG. 1. The cooperative effect of these potentials then result in electrons being collected primarily on those back surfaces 50 of the electrodes 44-47 which are not facing the beam path or source.

It can be seen from FIG. 2 that the electrodes do not intercept the beam or beam path or project into the path because collection of electrons is not dependent on intercept kind of collection on those surfaces 51 facing the beam. It is to be expected however that some electrons will strike and be collected on these front surfaces. This front collection would be secondary with respect to back collection considering the greater extent or degree of collection at these back surfaces. Furthermore, those electrons which are released by secondary emission at the frontsurfaces are quickly collected because of the close presence ofa more positive electrode. The electrons which are collected on the back surfaces 50 have previously reached the height or apex of their trajectories or have just passed through essentially zero forward velocity as measured axially along the beam. These electrons are also at a relatively low velocity in their lateral or radial directions.

FIG. 3 shows another embodiment of this invention where the collector electrodes 52-55 define a petal opening configuration with supporting parts thereof 56-59 extending parallel to the electron beam path and reflecting electrode 60.

FIG. 4 illustrates a further embodiment of this invention wherein collector electrodes 61-65 are arcuate members whose central apertures define a beam path. The housing 66 is formed by means of a plurality of metal channel rings 67 which are placed in stacked array as illustrated and welded to provide an evacuable structure. Lead in seals such as seals 49 for each of the rings provide a separate electrical connection for each electrode. A ceramic insulator means 68 also insulates each electrode from its respective ring.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A method of collecting electrons from an electron beam in an electron beam device comprising a. arranging a plurality of collector electrodes, having front and back surfaces, in a row along said beam with the front surfaces of said electrodes being first approached by said beam and back surfaces exposed to said beam after passing by said electrodes b. providing different voltages for said electrodes so that each electrode has a more positive potential than the subsequent electrode in the direction of the beam path providing a reflecting electrode projecting into said beam impressing a voltage on said reflecting electrode which is more negative with respect to said collector electrodes, whereby most of the electrons from said beam are caused to take up a radially curving trajectory to impinge on the rear surfaces of said collector electrodes.

2. In a reflex electron collector for an electron beam device the combination comprising a. A plurality of collector electrodes positioned along said beam b. said electrodes having front and back surfaces with respect to passage therealong of said beam c. means to impress voltages on said electrodes more negative than the preceding electrode in the direction of the beam, including a portion projecting toward the beam path d7 a reflector electrode for said beam e. means to impress a voltage on said reflector which is different from a voltage impressed on said collector electrodes so that the said voltages provide a reflecting action on electrons in said beam and most of said electrons are caused to impinge on said collectors on their back surfaces. 3. A reflex electron collector for an electron beam device comprising in combination a. a collector housing b. a series of axially spaced collector electrodes in said housing c. insulating means insulating said collector electrodes from one another for application of different potentials thereto more negative than the preceding electrode in the direction of the beam d. said electrodes having a front surface generally facing into said beam and a back surface c. said electrodes defining an opening therethrough to admit said electron beam f. a reflecting electrode member in said housing comprising a spike member projecting coaxially into said defined opening so that with a proper potential applied thereto which is negative with respect to said collector electrodes electrons from said beam are caused to take up a radial curving trajectory to impinge on said back surfaces ofsaid electrodes.

4. A reflex electron collector for an electron beam device comprising a. a housing member in receiving relationship with respect to said beam b. a projecting reflector electrode in said housing and projecting into said beam path an extended array of apertured dishlike collector electrode members in said housing and coaxially surrounding said beam path d. said collector electrodes being in a row along said beam path starting at said reflector electrode with a front surface being flrst approached by said beam in passing therethrough and a back surface being exposed to said beam after beam transversal therethrough e. electrical insulating means insulating said electrodes from each other and said reflector electrode from said housing so that voltages, each more negative than that applied to a preceding electrode. may be applied thereto to reflect electrons from said reflector electrode and collect said electrons on the back surfaces of said collector electrodes.

5. The invention as recited in claim 4 wherein at least three collector electrodes are employed in a row extending from the reflector electrode along the beam path.

6. The invention as recited in claim 5 wherein said collector electrodes are concave with respect to the direction of said beam.

7. The invention as recited in claim 5 wherein at least two of said collector electrodes are frustoconical.

8. The invention as recited in claim 5 wherein the axial spacing between collector electrodes along the beam path becomes greater in the direction ofthe beam.

9. The invention as recited in claim 5 wherein the reflecting electrode is coaxial with and surrounded by a least one of said collector electrodes.

10. The invention as recited in claim 5 wherein the apertures of said collector electrodes become larger in the direction of the beam path.

11. The invention as recited in claim 10 wherein said reflecting electrode is a narrow conelike member extending with its smaller end into the beam path to be surrounded by at least one of said electrodes.

12. The invention as recited in claim 8 wherein said reflector electrode is surrounded by one of said collector electrodes.

13. The invention as recited in claim 5 wherein at least two of said collector electrodes have different shapes.

14. A kl stron device comprising in combination a. a cat ode to generate an electron beam passing through the said klystron b. a series of cavity resonators along said beam to modulate said beam and an electron collector assembly to collect electrons from said beam after interaction in said resonators d. insulating means electrically insulating said collector from said klystron e. a row series of concavelike collectors having apertures therethrough to define a beam path and positioned concentrically with said path and in said collector said collector electrodes having front concave surfaces first approached by said beam in passing therethrough and rear convex surfaces exposed to said beam after transversal through a said collector electrode insulating means electrically insulating said collector electrodes from each other and said collector electrodes from said collector a projecting tapered cone reflector electrode in said collector assembly and projecting oppositely to said beam cup-shaped shield means in said collector and in coaxial surrounding relationship to said reflector electrode and said collector electrodes j. means insulating said shield from said collector and electrodes therein insulating means insulating said reflector electrode from said collector whereby different negative potentials may be applied between said reflector electrodes in increasing negative increments in a direction towards the said reflector electrode, and between said reflector electrodes and said collector electrodes any said beam becomes radially dispersed and most electrons therefrom are collected on the back surfaces of said collector electrodes. 

1. A method of collecting electrons from an electron beam in an electron beam device comprising a. arranging a plurality of collector electrodes, having front and back surfaces, in a row along said beam with the front surfaces of said electrodes being first approached by said beam and back surfaces exposed to said beam after passing by said electrodes b. providing different voltages for said electrodes so that each electrode has a more positive potential than the subsequent electrode in the direction of the beam path c. providing a reflecting electrode projecting into said beam d. impressing a voltage on said reflecting electrode which is more negative with respect to said collector electrodes, whereby most of the electrons from said beam are caused to take up a radially curving trajectory to impinge on the rear surfaces of said collector electrodes.
 2. In a reflex electron collector for an electron beam device the combination comprising a. A plurality of collector electrodes positioned along said beam b. said electrodes having front and back surfaces with respect to passage therealong of said beam c. means to impress voltages on said electrodes more negative than the preceding electrode in the direction of the beam, including a portion projecting toward the beam path d. a reflector electrode for said beam e. means to impress a voltage on said reflector which is different from a voltage impressed on said collector electrodes so that f. the said voltages provide a reflecting action on electrons in said beam and most of said electrons are caused to impinge on said collectors on their back surfaces.
 3. A reflex electron collector for an electron beam device comprising in combination a. a collector housing b. a series of axially spaced collector electrodes in said housing c. insulating means insulating said collector electrodes from one another for application of different potentials thereto more negative than the preceding electrode in the direction of the beam d. said electrodes having a front surface generally facing into said beam and a back surface e. said electrodes defining an opening therethrough to admit said electron beam f. a reflecting electrode member in said housing comprising a spike member projecting coaxially into said defined opening So that with a proper potential applied thereto which is negative with respect to said collector electrodes, electrons from said beam are caused to take up a radial curving trajectory to impinge on said back surfaces of said electrodes.
 4. A reflex electron collector for an electron beam device comprising a. a housing member in receiving relationship with respect to said beam b. a projecting reflector electrode in said housing and projecting into said beam path c. an extended array of apertured dishlike collector electrode members in said housing and coaxially surrounding said beam path d. said collector electrodes being in a row along said beam path starting at said reflector electrode with a front surface being first approached by said beam in passing therethrough and a back surface being exposed to said beam after beam transversal therethrough e. electrical insulating means insulating said electrodes from each other and said reflector electrode from said housing f. so that voltages, each more negative than that applied to a preceding electrode, may be applied thereto to reflect electrons from said reflector electrode and collect said electrons on the back surfaces of said collector electrodes.
 5. The invention as recited in claim 4 wherein at least three collector electrodes are employed in a row extending from the reflector electrode along the beam path.
 6. The invention as recited in claim 5 wherein said collector electrodes are concave with respect to the direction of said beam.
 7. The invention as recited in claim 5 wherein at least two of said collector electrodes are frustoconical.
 8. The invention as recited in claim 5 wherein the axial spacing between collector electrodes along the beam path becomes greater in the direction of the beam.
 9. The invention as recited in claim 5 wherein the reflecting electrode is coaxial with and surrounded by a least one of said collector electrodes.
 10. The invention as recited in claim 5 wherein the apertures of said collector electrodes become larger in the direction of the beam path.
 11. The invention as recited in claim 10 wherein said reflecting electrode is a narrow conelike member extending with its smaller end into the beam path to be surrounded by at least one of said electrodes.
 12. The invention as recited in claim 8 wherein said reflector electrode is surrounded by one of said collector electrodes.
 13. The invention as recited in claim 5 wherein at least two of said collector electrodes have different shapes.
 14. A klystron device comprising in combination a. a cathode to generate an electron beam passing through the said klystron b. a series of cavity resonators along said beam to modulate said beam c. and an electron collector assembly to collect electrons from said beam after interaction in said resonators d. insulating means electrically insulating said collector from said klystron e. a row series of concavelike collectors having apertures therethrough to define a beam path and positioned concentrically with said path and in said collector f. said collector electrodes having front concave surfaces first approached by said beam in passing therethrough and rear convex surfaces exposed to said beam after transversal through a said collector electrode g. insulating means electrically insulating said collector electrodes from each other and said collector electrodes from said collector h. a projecting tapered cone reflector electrode in said collector assembly and projecting oppositely to said beam i. cup-shaped shield means in said collector and in coaxial surrounding relationship to said reflector electrode and said collector electrodes j. means insulating said shield from said collector and electrodes therein k. insulating means insulating said reflector electrode from said collector whereby different negative potentials may be applied between said reflector electrodes in increasing negatIve increments in a direction towards the said reflector electrode, and between said reflector electrodes and said collector electrodes any said beam becomes radially dispersed and most electrons therefrom are collected on the back surfaces of said collector electrodes. 